Signal and Data Transport

What do we mean when we refer to Signal and Data Transport (SaDT) in the SKA design?

The “Signal and Data Transport” (SaDT) element includes all hardware and software necessary for the transmission of data and information between the Elements of the SKA. SaDT also includes the provision of timing which is critical for interferometry.

Installation of optic fibre during construction of the ASKAP antennas and associated infrastructure in 2011.Image courtesy Shaun Amy/CSIRO

More about the SaDT Consortia

Signal and data transport is the backbone of the SKA telescope. The Signal and Data Transport (SaDT) Consortium is responsible for the design of three data transport networks. These include the Digital Data Backhaul (DDBH) that transports signals from the radio telescopes to the Central Signal Processor (CSP), and data products from the CSP to the Science Data Processor (SDP) and from the SDP to the regional SKA Data Centres. The total data rates are very high, approximately 80 Tb/s for the DDBH links and another 80Tb/s for the CSP links. (Tb/s – Terabits per second)

The SaDT Hierachy – Click to enlarge (c) SKA Organisation

What makes up the SaDT?

Also covered by the SaDT is the Synchronisation and Timing (SAT) that provides frequency and clock signals from a central clock ensemble to all elements of the system to maintain phase information to the required accuracy for all receptors, and timing signals for data identification and time critical activities at the receptors, and the CSP and SDP. To maintain phase coherence across the array requires short-term timing precisions of around 1pico-sec, while for the requirements for pulsar timing experiments require 10nano-secs accuracies over 10 year periods. The timing is critical to the functionality of the SKA to work as a unified large telescope using a technique known as interferometry.

The final part of the SaDT is the Monitor and Control (M&C) that transmits and receives monitoring and control information throughout the system and includes the Telescope Manager (TM), itself comprised of three logical networks: Production Network, Engineering Network and Safety Network, the Network Manager (NMGR), as well as local monitoring and control.

Installation of optic fibre during construction of the ASKAP antennas and associated infrastructure in 2011. Image courtesy of Shaun Amy/CSIRO

Installation of optic fibre during construction of the ASKAP antennas and associated infrastructure in 2011. Image Shaun Amy/CSIRO

What the SaDT consortia will deliver?

Synchronisation and Timing: An ensemble of clocks, probably hydrogen masers, which can be linked to world timing standards; a method distributing timing, phase and frequency signals across 100km distances to the required level of accuracy, probably incorporating some level of measurement of the time for the signal to travel down the fibre and then a method for compensating for any changes introduced by e.g. temperature drifts.

Telescope Manager: A network that allow for monitoring of all the various sub-systems that comprise the SKA telescope and also allows for experiment specific control signals to be distributed throughout the system. TM will also comprise a safety network which will put the telescope into safe mode in case of failure.

What is the background of the consortium members?

The University of Manchester is the lead organisation in the SaDT consortium. Through the e-MERLIN and other projects, it has great experience in the two key fields for SADT: transporting high volumes of telescope data over distances in excess of 100km; and providing sufficiently accurate clock signal distribution that the whole array is phase coherent.

In addition, there is a great breadth of critical expertise contributed by other partners in the consortium, particularly built up through work on SKA pathfinders and precursors. SKA-Africa and CSIRO are building the MeerKAT and ASKAP telescopes respectively, both of which are facing SaDT issues on scales relevant to the SKA. In addition, both institutes offer essential knowledge of the two sites on which SKA is to be built.

Further experience is available in specific area from experts from other consortium members. GÉANT, AARNeT and SANReN are world leaders in providing high data rates over very long distances and are key advisors in assessing how to provide astronomers with access to telescope data. NPL is the UK’s National Measurement Institute and will lead the work on providing the clocks needed to meet the SKA requirements. NNMU, JIVE, UGranada, Tsinghua and Peking Universities are experts in the distribution of this timing information. NCRA and Tata Consulting Services are leading the whole Telescope Manager (TM) work package and so are ideal for designing the SaDT network supporting TM. IT offers state-of-the-art testing facilities for verifying our prototype systems.

Who is involved?

The Science and Data Transport consortium is led by Dr Keith Grainge of the University of Manchester, UK.

The institutions involved in the Signal and Data Transport consortium include